This study dealt with molding of natural composites using granular materials and naturally derived resin using vacuum-assisted resin transfer molding (VaRTM). The VaRTM process is a variation of vacuum-infusion RTM in which one of the solid tool faces is replaced by a flexible polymeric film. The VARTM process is a very clean and economical manufacturing method and suitable for the production of the large-size structure. Bamboo tips were used as reinforcements. Bamboo culm only and mixture of culm and leaf were crushed finely or roughly, which result in the four types of reinforcements. Bending, vibration and heat transfer characteristics were measured and the possibility of the application to wall material was examined.

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Natural fiber reinforced composite materials attracts attention because of a present global environment problem. Continuous natural fiber reinforced thermoplastic composites have superior mechanical property and have often been expected as structural materials. However, it is difficult to impregnate reinforcement fibers with thermoplastics because of high viscosity of melt of plastics. In this study, continuous fiber reinforced thermoplastic composites were obtained using intermediate materials fabricated through the Micro-Braiding technique. In this study uses, hemp and poly (lactic acid) (PLA) fibers were used as reinforcement and matrix, respectively. Composite plates were fabricated by hot press molding under various molding conditions, including molding temperature, pressure and time. Evaluation of mechanical properties were conducted. The relationship between the molding conditions and the mechanical properties of hemp fiber/PLA composite was obtained. It was clarified that molding temperature was most influence factor in a molding conditions.

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Today, CFRP composite vessels are used as fuel containers of CNG (Compressed Natural Gas) vehicles and fuel-cell vehicles. It is known that material property and fatigue life of CFRP composite vessels are seriously reduced by out-of-plane loading. Also, autofrettage treatment for the improvement of the fatigue life is conducted on composite vessels. The main objective of this study is to evaluate effects of autofrettage on damage behavior subjected to impact loading. Composite vessels used in this study consisted of aluminum liner fully wrapped by carbon/epoxy, which were fabricated by filament winding method. Impact tests and damage observation were performed on the composite vessels with and without autofrettage. Internal pressure test were also conducted after impact tests, and to investigate residual strength. As a result, absorbed energy of composite vessels with autofrettage became smaller than composite vessels without autofrettage. In composite vessels with autofrettage, delamination was suppressed, and residual burst strength became larger. It was clarified that CFRP composite vessels with autofrettage were superior in the impact resistance.

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The present paper discusses the degradation mechanism for weatherability flexural properties of CFRP subjected to the steady load and unload of the accelerated and the outdoor exposures. One of the specimens is made of epoxy resin and unidirectional carbon fiber prepregs having the fiber orientation angles of 0 and 90 degree, respectively and another specimen is made of the same epoxy resin only as the matrix of the prepregs. In order to clarify the effects of exposure period on the variations of flexural strengths and moduli, matrix volume fractions, thickness and absorption rate of infrared rays, the complex accelerated exposure test was conducted to continue for up 100 cycles and a direct outdoor exposure has been also conducted to continue for 13 years. It is shown that both the weatherability flexural strength can be calculated by the results of epoxy resin and thickness change of CFRP during the exposures, and these calculations are agreed with the experimental ones under the accelerated and the outdoor exposures.

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In the present study, in order to improve interfacial strength between Poly(L-Lactic Acid) (PLLA) and β-tricalcium phosphate (β-TCP), R-TCP surface was treated by 6 g, 12 g and 24g of L-lactic acid solution. The amount of L-lactic acid on β-TCP surface was determined by thermal gravimetric analysis (TGA). β-TCP/PLLA compound was obtained by kneading and specimens were fabricated by hot-pressing. Compared with non-treated β-TCP/PLLA composites, tensile strength of composite of β-TCP treated using 6g L-lactic acid was reduced. On the other hand, tensile strength of composite ofβ-TCP treated using 12 g L-lactic acid increased. Interfacial treatments do not affect modulus of elasticity. β-TCP/PLLA compounds were also processed using solution-dispersion method. Since non-treated β-TCP could be dispersed in solvent, tensile strength of non-treated β-TCP/PLLA by solution-dispersion was higher than that of composite fabricated by kneading.

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Bioactive ceramics/poly-L-lactic acid (PLLA) composites have been expected as a material for the bone fracture fixations which have more biocompatibility than monolithic PLLA. In this study, β-tricalcium phosphate (β-TCP)/PLLA composites containing three different β-TCP contents and monolithic PLLA specimens were prepared by injection molding and tested to clarify the effect of hydrolysis and strain rates on the mechanical properties. These specimens were immersed in phosphate buffered solution, and then compressive tests were performed at the strain rates ranging from 10^<-3> to 10^<-1> /s. In the results of these tests, both β-TCP/PLLA composites and PLLA specimens showed that their modulus have no dependence on the strain rate and their peak stress increased with increasing strain rates. After 16 weeks immersion, peak stress of specimens were decreased slightly. After 24 weeks immersion, peak stress of non-annealing PLLA specimens were decreased with increasing strain rates at strain rate of 10^<-1>/s.

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The applications of the conventional bioabsorbable bone fixations are limited to low loaded region, because of their lower mechanical characteristics. In this study, poly-L-lactide (PLA) that is one of the bioabsorbable plastic is molded into screw shape, and the mechanical characteristics of the PLA screw are investigated. The PLA screw is prepared by forging a bar made by push-out molding. The effect of push-out molding condition on the stretching length is evaluated. It was observed that the PLA screw could be stretched in case of molding temperature more than 100℃. The mechanical properties, such as the pulled out strength, the shearing strength, and the twist strength were measured. Crystallinity was also measured. The result of the measurement was compared with that of forged screws. It was confirmed that the molecular orientation in the screw by extrusion was different from the screw by forging. Therefore the shearing strength of the screw of extrusion is higher than that of the screw of forging by 12.2 MPa.

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Vinylester resin containing styrene is used for the materials reclaiming sewerage pipes. However, styrene is limited to use due to environmental problem in fabrication. Therefore, alternative resin is desired. Since sewerage pipes is subjected to soil pressure for a long time in service, long period creep property should be estimated in advance. In the present study, long period creep properties of vinylester resin containing monofunctional methacrylate as a candidate of alternative resin were evaluated. Short term creep tests under higher temperature were carried out and master curves were obtained using time-temperature superposition principle (TTS). We estimate the applicability of TTS for vinylester resins comparing with the results of 1,000 hour creep tests under room temperature. The results showed that TTS could be applicable for vinylester resins and the resins containing monofunctional methacrylate (monomer/ester=1.0/1.5, 1.5/1.0) had higher durability than conventional one.

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Fiber reinforced thermo-plastic composite materials offer significant potential advantages comparing thermo-set composites, including higher damage tolerance, unlimited shelf life, faster component manufacturing times, greater recyclability and improved work environment. However, it is generally difficult to properly impregnate fiber reinforcements during the manufacturing process, because of extreme high viscosity of the thermo-plastic matrix materials compared to that of thermo-set resins. Due to these difficulties in resin impregnation, intermediate materials using Micro-Braiding technique have been developed. In this study, process parameter investigations were carried out to determine the most suitable values of pressure, temperature and time for resin impregnation during molding. Impregnation was evaluated by observing cross-sectional surface. Impregnation ratio increased with molding pressure, time and temperature. Especially, molding pressure was more effective on impregnation. It is confirmed that effect of molding temperature on impregnation was less comparing to that of others.

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The interfacial strength in a glass fiber/epoxy composite is evaluated by using the cruciform specimen method. To find the relation between the tensile and shear stresses at interfacial debonding, the angle between the fiber and the loading directions are changed. Moreover, stress analysis using finite element method (FEM) is conducted. Based on the experimental and the analytical data, the interfacial failure criterion is developed. And then the relation between the interfacial normal and shear stress at debonding initiation is discussed.

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Foam core sandwich structures are integral constructions consisting of two composite facesheets and a lightweight foam core. Since they have excellent mechanical properties, application of foam core sandwich structures to primary aircraft structures is highly expected. However, since the composite facesheet is very thin and the lightweight foam core is weak, they can be easily damaged when an impact or indentation load is applied. The facesheet locally deflects and the core is crushed. A residual dent induced by the core crushing significantly degrades the mechanical properties of the foam core sandwich structure. However, underlying mechanism of the residual dent formation is not sufficiently clarified. This study investigated quasi-static indentation response of foam core sandwich beams. First, the indentation loading-unloading response and the subsequent relaxation behavior were evaluated using quasi-static indentation tests. The indentation behavior was then analyzed by extending a "segment-wise model", which was formulated for honeycomb sandwich beams in a previous study. It was shown that the reaction force from the core to the facesheet controls the residual dent formation and that the relaxation behavior of the facesheet dent can be predicted by considering the stress relaxation of the crushed core.

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Nitrides, especially titanium nitride (TiN), aluminum nitride (AlN), and titanium aluminum nitride (TiAlN) have been studied for their novel characteristics. TiN with gold color is used as thin film coating for cutting tool materials due to high hardness, AlN has relatively good thermal and electrical conductivity and is used for heat sinks and similar applications. TiAlN has excellent hardness and oxidation resistance and is used for cutting tools. However, there are many difficulties for synthesizing these nitrides such as microparticulation, extended synthesis time, low purity and high production cost in manufacturing process. An electrical wire explosion technique has been studied for synthesizing nano sized ceramics powders by many researchers. This technique has also been applied for synthesizing TiN powders in liquid nitrogen in our previous work, and nano sized and high purity powders could be recovered in moderate conditions. In the present investigation, titanium wire andaluminum wire were used for synthesizing TiN, AlN and TiAlN. By changing the conditions, the reactivity was clearly changed, and TiN and AlN were successfully recovered in moderate conditions. In the experiment of synthesizing TiAlN, it was not recovered but TiN, AlN and TiAl were recovered. The recovered powders were composed of spherical fine particles in the order of nano-meter. The particle size was observed using scanned electron microscopes (SEM) and the recovered powders were characterized through the X-ray diffraction (XRD).

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In this present investigation, a new approach for synthesizing intermetallic nitrides using metal jet has been developed. A metal jet induced from a conical shaped charge has been directed into liquid nitrogen. The source of the metal jet was aluminum, and it was penetrated into titanium powders submerged in liquid nitrogen. SEP, an explosive produced by Kayaku Japan Co. Ltd, was set on the aluminum cone, and this explosive was detonated by electric detonator placed on the top of the cone. In prior research, the metal jet velocity was estimated as 6km/s. This research investigated a range of separation distances between the cone and the target material. At the moderate condition, some bulk materials, which were composed of intermetallics like titanium nitride (TiN) and titanium aluminum nitrides (Ti_2AlN, Ti_3AlN), were recovered. The samples recovered were characterized for the microstructure using optical and scanned electron microscopes (SEM), and electron probe microanalyzers (EPMA).

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The mechanisms of reflection and transmission of elastic stress pulses in a one- dimensional structural member at discontinuities have long been a subject of interest in impact dynamics, which find many applications. In the present work, experimental data on the reflection and transmission of longitudinal elastic stress pulses at a discontinuity of two dissimilar circular bars are presented and compared with predictions from one-dimensional elastic wave propagation theory. The effects of cross section and impedance ratios on the stress and energy reflection and transmission coefficients are examined over a limited range of cross section and impedance ratios.

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The dynamic compressive properties of starch-based biodegradable plastics were measured over a wide range of strain rates from 10^<-4> to 10^<-3> s^<-1> by using a split Hopkinson pressure bar method. In addition, compressive and tensile static stress-strain curves of starch-based biodegradable plastics were measured at a strain rate of 10^<-3> s^<-1>. We determined constants of Drucker-Prager yield criterion for starch-based biodegradable plastics, and drew the yield curves in the second deviatoric stress and invariant-first invariant of stress. The compressive yield stress is dependent upon the strain rate.

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With a view to examine the axial crushing behavior of thin-walled structures, which are used as energy-absorbing components of transports under various dynamic compressive loads, the axial crushing behaviour of some thin-walled regular polygonal tubes were investigated. This study was focused on the buckling modes of thin-walled polygonal tubes and the effects of buckling mode and cross-sectional geometry (the number of apexes and the thickness) on the performance of tubes, which was evaluated primarily by the absorbed energy per unit volume. The effect of impact velocity on the absorbed energy per unit volume was also studied.

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In near future, the regulation for Pb as an alloy component, such as the RoHS directive, will be severer. So far, many types of non Pb added free-cutting steels have been appeared. But in order to utilize new free-cutting steels, it is necessary to know the mechanical properties of conventional Pb added free-cutting steels. In the past, dynamic and quasi-static mechanical properties for virgin specimen of Pb added SUM24L (JIS G 4804: 2008, equivalent to AISI 12L14 steel) were acquired by tensile tests at strain rates of 1×10^3s^<-1> and 1×10^<-3>s^<-1>, respectively, at room temperature. In the present paper, the same tests were carried out for pre-fatigued specimens. This loading combination, fatigue and impact, simulates a certain service condition, normal operational loading and accidental dynamic loading. As a result, the degradation of mechanical properties was not so large.

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Micro/Nano-satellites with less than 50kg have been recognized recently as new promising tools for space development and utilizations with their extreme low cost and short development period. In Japan, many universities including university of Tokyo have been developing nano-satellites (less than 20kg) for educational objectives, starting with success of lkg CubeSat launched in 2003, and more sophisticated satellite such as CUTE-1.7+APD of Tokyo Institute of Technology or PRISM and Nano-JASMINE of University of Tokyo appeared recently which aim for practical missions such as world top level space sciences or low cost Earth observation. A new project just started in March 2010 in Japan funded by the government, seeking to establish all-Japan nano-satellite research, development and utilization consortium, which is expected to open a new way of low cost and fast space development and utilization.

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